Background of the Invention
The invention relates to a wall segment for a combustion area to which a hot fluid can be applied, in particular for a combustion chamber in a gas turbine. The invention also relates to a combustion area.
A thermally highly stressed combustion area, such as a furnace, a hot-gas channel or a combustion chamber in a gas turbine, in which a hot fluid is produced and/or carried, is provided with a lining for protection against excessive thermal stress. The lining is composed of heat-resistant material and protects a wall of the combustion area against direct contact with the hot fluid, and the severe thermal stress associated with this.
U.S. Pat. No. 4,840,131 relates to improved attachment of ceramic lining elements to a wall of a furnace. A rail system, which is attached to the wall and has a number of ceramic rail elements by means of which the lining elements are held is provided in this document. Further ceramic layers may be provided between a lining element and the wall of the furnace, including a layer composed of loose, partially compressed ceramic fibers, which layer has at least the same thickness as the ceramic lining elements, or a greater thickness. The lining elements in this case have a rectangular shape with a planar surface and are composed of a heat-insulating, fire-resistant ceramic fiber material.
U.S. Pat. No. 4,835,831 likewise relates to the fitting of a fire-resistant lining on a wall of a furnace, in particular a vertical wall. A layer composed of glass, ceramic or mineral fibers is fitted to the metallic wall of the furnace. This layer is attached to the wall by metallic brackets or by adhesive. A wire mesh network with honeycomb meshes is fitted to this layer. The mesh network is likewise used to protect the layer composed of ceramic fibers from falling off. A continuous, closed surface composed of fire-resistant material is applied to the layer secured in this way, by means of a suitable spraying method. The described method largely avoids fire-resistant particles produced during the spraying process from being thrown back, as would be the case if the fire-resistant particles were sprayed directly onto the metallic wall.
A lining for walls of highly stressed combustion areas is described in EP 0 724 116 A2. The lining comprises wall elements composed of high-temperature-resistant structural ceramic, such as silicon carbide (SiC) or silicon nitride (Si3N4), which are mechanically attached by means of a fastening bolt to a metallic supporting structure (wall) of the combustion chamber. A thick insulation layer is provided between the wall element and the wall of the combustion area, so that the wall element is at a distance from the wall of the combustion chamber. The insulation layer, which is three times as thick as the wall element, is composed of ceramic fiber material, which is prefabricated in blocks. The dimensions and the external shape of the heat protection segments can be matched to the geometry of the area to be lined.
Another type of lining for a thermally highly stressed combustion area is specified in EP 0 419 487 B1. The lining is composed of heat protection segments, which are held mechanically on a metallic wall of the combustion area. The heat protection segments touch the metallic wall directly. In order to avoid excessive heating of the wall, for example by direct heat transfer from the heat protection segment or by the ingress of hot active fluid into the gaps formed by mutually adjacent heat protection segments, the area formed by the wall of the combustion area and the heat protection segment has cooling air, so-called sealing air, applied to it. The sealing air prevents the hot active fluid from penetrating as far as the wall, and at the same time cools the wall and the heat protection segment.
The object of the invention is to specify a wall segment for a combustion area, in particular a combustion chamber in a gas turbine, to which a hot fluid can be applied. A further object is to specify a heat-resistant combustion area.
The object relating to a wall segment is achieved according to the invention by a wall segment for a combustion area, to which a hot fluid can be applied, having a metallic supporting structure and having a heat protection element which is mounted on the metallic supporting structure. The metallic supporting structure is provided at least in places with a thin, heat-resistant separating layer, with the separating layer being fitted between the metallic supporting structure and the heat protection element. Alternatively or additionally, the object is achieved by a wall segment in which, according to the invention a metallic, heat-resistant separating layer is fitted at least in places between the supporting structure and the heat protection element. The metallic separating layer may be thin.
The invention is based on the knowledge that the heat protection segment and the wall of a combustion area are composed predominantly of relatively inelastic materials such as structural ceramic and metal. A disadvantage of a lining designed in such a way for a combustion area is that the heat protection elements directly touch the wall of the combustion area. For production reasons and owing to the different thermal expansion of the wall and the heat protection element, the heat protection element may not always be able to lie flat on the wall. In consequence, high forces may be produced locally at the contact points. If the heat protection element and the wall have different thermal expansion characteristics, it is possible in unfavorable conditions for the heat protection segments and/or the wall to be damaged due to the introduction of high forces at the contact points when the operating state of the combustion area changes, for example in the event of a load change in a gas-turbine system. In consequence, gaps between the heat protection element and the wall may be formed between the contact points of the heat protection element and the wall, where there is no contact. These gaps form access channels for hot fluid. In order to prevent the ingress of hot fluid, an increased amount of sealing air would be required in this situation between the wall and the heat protection element.
The refinement of a wall segment according to the invention has the advantage that a deformable separating layer inserted between the metallic supporting structure and the heat protection element can absorb and compensate for possible relative movements of the heat protection element and of the supporting structure. Such relative movements can be caused, for example, in the combustion chamber of a gas turbine, in particular an annular combustion chamber, by the materials used having different thermal expansion characteristics or by pulsations in the combustion area. This can occur in the even of irregular combustion to produce the hot active fluid or as a result of resonance, for example. At the same time, the separating layer results in the relatively inelastic heat protection element lying flatter on the separating layer and on the metallic supporting structure overall, since the heat protection element penetrates into the separating layer in places. The separating layer can thus also compensate for irregularities, due to production effects, on the supporting structure and/or on the heat protection element, which can lead to disadvantageous introduction of forces at specific points, locally.
The heat-resistant separating layer inserted between the heat protection element and the metallic supporting structure can advantageously be deformed elastically and/or plastically by the heat production element. The heat protection element can thus penetrate into the heat resistant separating layer in places, and deform it, and compensate for irregularities in the contact surface of the heat protection element and/or of the supporting structure due to production effects and/or occurring as a result of operation of the system. Forces can thus be introduced over a larger area to the largely inelastic heat protection element, overall. Thus, the risk of damage to the heat protection element and/or to the metallic supporting structure is less than when forces are introduced via the direct contact, which occurs at specific points at least in places, between the heat protection element and the supporting structure. The deformation of the separating layer in places by the heat protection element also leads to a reduction in the gap openings between the heat protection element and the separating layer, which reduces the flow of hot fluid behind the heat protection element. In order to avoid, or at least reduce the flow behind the heat protection elements, sealing air can be applied to a cavity formed by the heat protection element and the metallic supporting structure. The requirement for sealing air is decreased by reducing the gap openings and reducing the size of the cavity volume by means of the separating layer.
The separating layer preferably has a thickness which is less than the height of the heat protection element. The expression height of the heat protection element in this case refers to the extent of the heat protection element in the direction at right angles to the surface of the metallic supporting structure. The height may in this case correspond directly to the layer thickness of the heat protection element. In the case of a domed, curved or cap-shaped heat protection element, the height is, in contrast, greater than the wall thickness of the heat protection element. The separating layer may have a layer thickness of up to a few millimeters. The layer thickness is preferably less than one millimeter, in particular up to a few tenths of a millimeter.
The heat-resistant separating layer preferably comprises a metal grid with honeycomb cells, which grid can be deformed by the heat protection element. The honeycomb cells of the metal grid are advantageously filled with a deformable filling material. The honeycomb cells may be produced from thin metal sheets, with a thickness of only a few tenths of a millimeter, for example from a nickel-based alloy. The filling material is preferably in the form of powder and is formed from a metal and/or a ceramic. The ceramic powders can be heated and transported in a plasma jet (atmospheric plasma spray). Depending on the nature of the powder and the spraying condition, a layer produced by the powder can be formed with a greater or lesser number of pores. The honeycomb cells are preferably filled with a porous layer, which can thus be deformed easily and provides good insulation. A metallic filling material is preferably formed from a heat-resistant alloy as is also used, for example, for coating gas turbine blades. A metallic filling material is formed, in particular, from a base alloy of the MCrAlY type, in which case M may be nickel, cobalt or iron, Cr chromium, Al aluminum and Y yttrium or some other reactive rare-earth element. During the deformation and penetration of the heat protection element into the separating layer, the deformable filling material closes the gap openings which exist between the contact surfaces, or reduces their size, which leads to a reduction in the requirement for sealing air. Furthermore, the separating layer reduces the volume of the cavity formed by the heat protection element and the supporting structure, as a result of which the requirement for sealing air is further reduced. In a gas turbine, the active fluid can furthermore be cooled by the cooler sealing air when said sealing air enters the combustion area, which can lead to a reduction in the overall efficiency of a gas turbine system being operated using the hot active fluid. The reduced requirement for sealing air in this case also leads to less reduction in overall efficiency than would be the case in a gas turbine system with heat protection elements but without a separating layer.
The heat-resistant separating layer may also advantageously comprise a felt composed of thin metal wires. Such a metal felt may also be laid on contours having very small radii of curvature. Thus, it is particularly suitable as a separating layer for a supporting structure with an irregular shape in a combustion area, for example a metallic supporting structure for holding heat protection elements, to which sealing air is applied, in the combustion chamber of a gas turbine. The thickness of the metal felt is chosen such that even relatively large gap openings between two contact surfaces of a heat protection element and the supporting structure can be closed, or at least greatly reduced in size, by the metal felt. It is thus possible to use a wall segment designed in such a way even in systems in which the amount of sealing air available is limited.
If the gap openings which result between the metallic supporting structure and the associated heat protection elements are relatively small and uniform, then the heat-resistant separating layer is preferably applied as a thin coating to the metallic supporting structure.
In order to make it possible to withstand the loads resulting from the ingress of hot fluid and to protect the metallic supporting structure effectively, the heat-resistant separating layer installed between the supporting structure and the heat protection element is designed to be scale-resistant at a temperature of more than 500xc2x0 C., in particular up to approximately 800xc2x0 C.
The heat protection element is advantageously mechanically connected to the metallic supporting structure of the combustion area. The contact force which the mechanical retention exerts on the heat protection element in the direction of the supporting structure, and thus the penetration depth of the heat protection element and the deformation of the heat-resistant separating layer, can be adjusted by means of a mechanical joint. The remaining gap openings and the requirement for sealing air which results from them can thus be matched to the operating conditions and to the amount of sealing air available at the respective point of use.
The heat protection element is advantageously held on the supporting structure by means of a bolt. The bolt acts approximately in the center of the heat protection element, in order to introduce the contact force as centrally as possible into the heat protection element. The heat-resistant separating layer has a recess in the region in which the bolt of the associated heat protection element is attached to the metallic supporting structure. Further recesses and openings in the separating layer, in particular in a gas turbine, are likewise provided wherever the supporting structure has channels for supplying sealing air into the cavity formed by the heat protection element and the supporting structure. Sealing air can thus flow into the cavity, thus making it possible to prevent the hot active fluid from flowing behind the heat protection elements and/or the separating layer.
The heat protection element can preferably also be mechanically held against the metallic supporting structure by means of a tongue-and-groove joint.
The object relating to a combustion area is achieved, according to the invention, by a combustion chamber forming a combustion area, in particular a combustion chamber in a gas turbine, which is formed from wall segments described above. In order to provide a heat-resistant lining for the combustion area, heat protection elements are fitted on a metallic supporting structure of the wall segment. The heat protection elements are, for example, in the form of flat or curved polygons with straight or curved edges, or of flat, regular polygons. They completely cover the metallic supporting structure which forms the outer wall of the combustion area, except for expansion gaps provided between the heat protection elements. Hot fluid can penetrate into the expansion gaps only as far as a heat-resistant separating layer on the wall segment, and cannot flow behind the heat protection elements. Mechanical holders for the heat protection elements, and the metallic supporting structure, are thus largely protected against being damaged by hot fluid.